The present invention relates to earth-moving machines, mainly to machines for laying horizontal drainpipes. In particular, the present invention relates to machines for laying drainpipes by the ditchless method.
The ditchless drainlayers of the present invention can be employed predominantly for constructing drainage systems in drainage and irrigation zones. They also prove useful for laying flexible pipelines or cables into the ground, particularly when it is required to ensure either a predetermined depth or gradient, or both.
It is common knowledge that drainpipes can be laid by means of drainlayers made as a chain ditch excavator working in conjunction with the drainlaying equipment. The active working element of such a drainlayer digs a more or less narrow ditch; the drainpipe is laid on the bottom of said ditch and the latter is then backfilled. Such a method of drainlaying inevitably calls for excavating and moving considerable masses of soil which causes relatively low drainlaying speeds and a low output, even with considerable powerful prime movers. Besides, this method of laying disturbs the integrity of the fertile layer of soil because clay, sand and other infertile materials are lifted to the surface and remain thereon.
These disadvantages have led to the advent of the ditchless method of drainlaying which finds an evergrowing application in the world's practice of land-reclamation and irrigation.
The essence of this method consists in that a passive working element made as a narrow pointed plow or cutter coupled to a sufficiently powerful prime mover penetrates into the ground to the required depth and cuts a narrow slit in the ground which is continuously filled with a drainpipe in the course of movement of the prime mover with the working element. The slit formed in the ground closes directly behind the cutter. This rules out the vertical movement of the soil almost completely, does not call for backfilling, does not interfere with the structure of the fertile layer of the soil and significantly increases the drainlaying speed several times.
These indisputable advantages as well as the manufacture of more and more powerful prime movers have resulted in the widespread employment of the machines for laying drains, cables, flexible pipelines, etc., by the ditchless method. The provision of such machines raises a number of problems caused by the specific features of this method of laying.
The most specific requirement for the drainage line consists in the accurate maintenance both of its depth at each point of the line and of the total preset gradient. If in the ditch-digging method these requirements can be checked (by instruments and even visually) and the impermissible errors can be timely corrected, the ditchless laying requires the provision of a system (preferably automatic) of controlling the height of the working element which would ensure the requisite accuracy of laying depth and gradient since no corrections or alterations are possible in ditchless laying of pipes.
In the course of drainlaying the prime mover, the working element is subjected to adverse effects, such as irregularities of the soil traversed by the prime mover, variations in the force of resistance to the movement of the cutter-type working element due to variations in the properties of the soil, unexpected obstacles, etc., also due to changes in the angular position of the working element.
The control elements and their operating systems are adapted to counter these adverse effects so as to minimize their influence on the laying accuracy. This problem involves, for one, speedy operation of the control system, i.e. prompt execution of the commands eliminating the effect of the encountered obstacles, preferably without delay or with a minimum delay.
Hence, the ditchless drainlayer must be coupled to a prime mover and controlled in such a manner that its working element or, more specifically, the cutting edge of the latter, would move along a required trajectory, forming the bottom of the slit to receive the drainpipe. At the same time it is necessary to retain a constant angular orientation of the working element.
Known in the prior art are machines of this type wherein the working element is mounted on a prime mover and, in the course of its positional control, rests wholly on the prime mover alone. Such a mounting of the working element hinders considerably the control of its angular position and height. The control, as has already been stated above, is intended to rule out the influence of chance changes in the position of the prime mover on the position of the working element. In this case the control system is excessively loaded, and the requirements for its high operational speed and protection against obstacles can be met only by making it highly complicated and, as a consequence, more expensive, less reliable and difficult to handle.
Therefore, the layout wherein the working element rests on the prime mover alone is used only in the machines which are not intended to ensure accurate maintenance of the depth and gradient, for example in rippers, stump pullers, cable layers, etc.
More profitable and promising are the ditchless drainlayers articulated to the prime mover and resting during the positional control of their working element not only on the prime mover but also on the ground, usually in the rear end of the working element.
Known in the prior art is a drainlayer wherein the cutter-type working element is articulated by a frame and a hydraulic cylinder with a prime mover while the height of the working element is controlled by an element in the form of an adjustable front edge of the working element. This adjustable element is connected with a hydraulic cylinder which, in turn, is controlled by the transmitter of the angular position of the working element via an amplifier-converter.
Such a drainlayer has only one control circuit and is vulnerable to the hindrances resulting from the irregularities of the ground surface traversed by the prime mover. The vertical motions of the prime mover disturb the angular position of the working element and restoring of this position by the angular position control system is not equivalent to maintaining the required digging depth at each particular point. In addition, the shifting of the working element to a new depth caused by the change in its angular position would be rather slow and takes place on a considerably long path which means that the system does not feature the required operational speed. This disadvantage is attributable to the presence of the adjustable element in the form of an adjustable front edge which, changing its angular position in the process of control, exerts no direct influence on the height of the working element, but only produces forces which turn it in the ground. Moreover, when the working element is inclined either directly or due to the turning of the front edge, this changes the ground cutting angle and thus disturbs the optimum working conditions of the working element, changes the cutting resistance and introduces new disturbances into the motion of the prime mover. Furthermore, in the process of control the working element may turn counterclockwise through such an angle at which the back angle disappears (the back angle is the angle between the rear edge of the cutter and the bottom of the slit); in this case the foot and the heel of the cutter-type working element will damage and distort the profile of the slit bottom which is unacceptable for drainlaying.
In other known drainlayers, the cutter-type working element rests on the bottom of the slit through a runner or shoe movably connected to the lower rear part of the cutter. The runner slides over the bottom of the slit being connected with the working element by a hydraulic cylinder and functions as a support for controlling the height of the working element. This support is independent of the prime mover which means that it receives the changes in its angle and height in motion. The use of the supporting runner ensures the required speed of action because the height of the cutter element is changed directly, without any intermediate elements which are responsible for the delay.
However, the use of the supporting runner brings about two new disadvantages. Firstly, resting on the slit bottom, the runner distorts it, especially so in case of loose soils, and thus diminishes the accuracy of laying the drainpipes. Secondly, being a one-sided support, the runner creates asymmetry of the "up-and-down" control of the working element. On the "down" command the runner may break away from the supporting surface and rise above it. When the working element penetrates into the ground the runner is inoperative and this penetration must take place under the weight of the working element and under the forces acting on the front edge of the cutter and other factors which are of an extremely irregular nature. An attempt to take these factors into account complicates considerably the layout of the control system and its optimum functioning.
In another type of prior art drainlayers, the cutter-type working element connected rigidly or movably to the frame is provided with carrying blades which can swivel relative to the working element, stick out on both sides from the cutter and cut into the slit walls during operation.
These blades are free from the disadvantages of the runner described above, since they constitute a two-sided support; however, being rotatably secured to the cutter with the turning axis located near the center of pressure (the fulcrum of the resultant force) they function as an integrating link and do not, therefore, feature the requisite speed of action which, as stated above, is a serious disadvantage of the system for controlling the position of the working element of the ditchless drainlayer.
Moreover, the blades of the known design prevent the cutter from being lifted when the prime mover is stopped which is extremely awkward in emergency situations or when the process of laying is completed close to an obstacle, such as a wall or the like.
Finally, the prior art devices prevent the possibility of regulating the dynamic characteristics of the system by changing the distance between the pivot of the control elements (e.g. blades) and the fulcrum of the resultant of the forces acting on the swivelling support. An increase in this distance could bring the properties of the swivelling blades close to those of the runner in respect of the speed of action while the adjustment of this distance is highly desirable for adapting the drain-layer to operation in various soils.